1. Field of the Invention
This invention relates to means for controlling the switching operation of apparatus of the type disclosed in co-pending applications Ser. No. 492,330, filed July 26, 1974 and Ser. No. 542,697, filed Jan. 21, 1975, both assigned to the assignee of the present case. In particular, the invention relates to means for controlling the operation of switching circuits so that, during both recording and reproducing, the polarity of the chrominance subcarrier will be reversed or not reversed during corresponding line intervals.
2. The Prior Art
In the system disclosed in the previously mentioned application Ser. No. 492,330, a switching circuit is provided to reverse the polarity of the chrominance signal when a color television signal is recorded. The polarity reversal takes place during alternate line intervals of signals recorded on alternate tracks on a recording medium. The polarity of the chrominance signal recorded on the interleaving tracks is not reversed during any line interval. The signals are also recorded in h-alignment which means that the synchronizing signals at the end of each line interval of each track are recorded so as to be aligned side by side with the recordings of synchronizing signals at the end of each of the line intervals of the next adjacent track.
Due to h-alignment and to the sequence of polarity reversals of the chrominance signals in alternate lines, the undesired cross-talk signal picked up from the next adjacent track when playing back the desired track can be minimized by passing the combined desired and cross-talk signals through a switching circuit that alternately reverses the polarity of successive line intervals of the chrominance signal and then passing the output signal of the switching circuit through a comb filter that adds the chrominance signals of two successive line intervals at a time. The switching circuit must be actuated so that it will reverse the polarity of alternate line intervals only during the reproduction of those tracks in which the polarity of the signals was reversed during recording and will not reverse the polarity of alternate line interval signals during the reproduction of those tracks in which the polarity was not reversed during recording.
In the system disclosed in the previously mentioned application Ser. No. 542,697, the switching circuit is connected to switch the polarity of only the chrominance subcarrier and not of the entire chrominance signal. The pattern of switching, whereby the polarity of the chrominance subcarrier is reversed at the end of each line interval during the recording of one track but not reversed during the recording of the next track, is still the same as in the apparatus disclosed in application Ser. No. 492,330.
It is one of the objects of the present invention to provide a circuit that responds automatically to the synchronizing signals and signals obtained due to rotation of the rotating transducer to select specific field intervals in which the polarity reversal is to take place. Polarity reversal during the remaining field intervals recorded on interleaving tracks will automatically be avoided.